Method of controlling transmit power of uplink channel

ABSTRACT

A method of controlling a transmit power of an uplink channel is provided. Downlink control information of which Cyclic Redundancy Check (CRC) parity bits are masked with a TPC identifier is received on a downlink control channel. The transmit power of the uplink channel is adjusted based on a TPC command in the downlink control information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. ProvisionalApplication Ser. No. 61/025,817, filed on Feb. 4, 2008, and KoreanPatent Application No. 10-2008-0049147 filed on May 27, 2008, each ofwhich is incorporated by reference herein in their entireties.

BACKGROUND

1. Technical Field

The present invention relates to wireless communications, and moreparticularly, to a method of controlling a transmit power in a wirelesscommunication system.

2. Related Art

Third generation partnership project (3GPP) mobile communication systemsbased on a wideband code division multiple access (WCDMA) radio accesstechnology are widely spread all over the world. High-speed downlinkpacket access (HSDPA) that can be defined as a first evolutionary stageof WCDMA provides 3GPP with a radio access technique that is highlycompetitive in the mid-term future. However, since requirements andexpectations of users and service providers are continuously increasedand developments of competing radio access techniques are continuouslyin progress, new technical evolutions in 3GPP are required to securecompetitiveness in the future.

To exchange data between a base station (BS) and a user equipment (UE)in the wireless communication system, there is a need to control atransmit power for a transmit signal. In particular, transmit powercontrol of an uplink channel is important in terms of power consumptionof the UE and service reliability. In uplink transmission, if a transmitpower is too weak, the BS cannot receive a transmit signal of the UE. Onthe contrary, if the transmit power is too strong, the transmit signalmay act as interference to a transmit signal of another UE, and mayincrease battery consumption of the UE.

A transmit power control (TPC) command is generally used to control atransmit power of a channel between the BS and the UE. In theconventional WCDMA system, the TPC command is used in both uplink anddownlink transmission. A dedicated physical uplink channel (DPCCH) is anuplink channel for carrying a TPC command for a downlink channel. Adedicated physical channel (DPCH) is a downlink channel for carrying aTCP command for an uplink channel. A structure of the DPCH may be foundin section 5.3.2 of the 3GPP TS 25.211 V7.0.0 (2006-03) “TechnicalSpecification Group Radio Access Network; Physical channels and mappingof transport channels onto physical channels (FDD) (Release 7)”. TheDPCCH and the DPCH are dedicated channels used only between a UE and aBS.

An evolved-UMTS terrestrial radio access network (E-UTRAN) system basedon orthogonal frequency division multiple access (OFDMA) is currentlybeing standardized. The E-UTRAN system is also referred to as a longterm evolution (LTE) system. Examples of downlink physical channels usedin the E-UTRAN include a physical downlink control channel (PDCCH) and aphysical downlink shared channel (PDSCH). Unlike the WCDMA system, thePDCCH is only one physical control channel in the E-UTRAN. The PDCCH cancarry dedicated control information for a UE or common controlinformation for all UEs in a cell. Examples of uplink physical channelsinclude a physical uplink control channel (PUCCH) and a physical uplinkshared channel (PUSCH).

In general, in order for a BS to transmit a TPC command to a UE, whenthe BS reports downlink resource allocation information and/or uplinkresource allocation information to the UE, the TPC command istransmitted on the PDCCH together with the reported information. Thedownlink resource allocation information is transmitted when there isdata to be transmitted by the BS to the UE. The uplink resourceallocation information is transmitted after the UE requests the BS toallocate resources. However, the TPC command cannot be transmitted tothe UE when neither the downlink resource allocation information nor theuplink resource allocation information is transmitted. For example, whenthe UE transmits or receives a voice over Internet protocol (VoIP)packet by using radio resources pre-allocated through semi-persistentscheduling, the UE may not be able to receive the TPC command sinceresource allocation information is unnecessary.

When only the TPC command is transmitted for power control to the UEthrough one type of PDCCH, radio resources may be ineffectively usedsince a size of the PDCCH is significantly large while a size of the TPCcommand is only several bits.

Accordingly, there is a need for a method capable of effectivelytransmitting a TPC command to a UE through a PDCCH.

SUMMARY

The present invention provides a method of controlling a transmit powerof an uplink channel in a wireless communication system.

The present invention also provides a method of transmitting a transmitpower control (TPC) command for controlling a transmit power.

In an aspect, a method of controlling a transmit power of an uplinkchannel in a wireless communication system is provided. The methodincludes receiving downlink control information on a downlink controlchannel, wherein the downlink control information comprises at least onetransmit power control (TPC) command and Cyclic Redundancy Check (CRC)parity bits of the downlink control information are masked with a TPCidentifier, and adjusting the transmit power of the uplink channel basedon the at least one TPC command.

In some embodiments, the downlink control channel may be a PhysicalDownlink Control Channel (PDCCH) and the uplink channel may be aPhysical Uplink Control Channel (PUCCH) or a Physical Uplink SharedChannel (PUSCH). The PUCCH and the PUSCH may use different TPCidentifiers. The TPC identifier may be received from a base station. Thesize of the TPC identifier may be 16 bits.

In some embodiments, The downlink control information comprises aplurality of TPC commands. The TPC command may be indicated by a TPCindex. The TPC index may be received from a base station.

In another aspect, an apparatus for wireless communication includes aRadio Frequency (RF) unit for transmitting and receiving radio signals,and a processor coupled with the RF unit and configured to receivedownlink control information on a downlink control channel, wherein thedownlink control information comprises at least one transmit powercontrol (TPC) command and Cyclic Redundancy Check (CRC) parity bits ofthe downlink control information are masked with a TPC identifier, andadjust a transmit power of an uplink channel based on the at least oneTPC command.

In still another aspect, a method of transmitting transmit power control(TPC) commands for controlling a transmit power of an uplink channel ina wireless communication system includes preparing downlink controlinformation which comprises a plurality of TPC commands, attachingCyclic Redundancy Check (CRC) parity bits to the downlink controlinformation, masking the CRC parity bits with a TPC identifier, andtransmitting the CRC-masked downlink control information.

In still another aspect, an apparatus for wireless communicationincludes a control channel generator configured to attach CRC paritybits to downlink control information which comprises a plurality of TPCcommands, and to mask the CRC parity bits with a TPC identifier, and atransceiver for transmitting the CRC-masked downlink controlinformation.

In still another aspect, an apparatus for wireless communicationincludes a RF unit for transmitting and receiving radio signals, and aprocessor coupled with the RF unit and configured to monitor at leastone downlink control channel by attempting decoding of the at least onedownlink control channel, and acquire a TPC command on a downlinkcontrol channel when no CRC error is detected in the downlink controlchannel, wherein the CRC parity bits in the downlink control channel aremasked with a TPC identifier.

In still another aspect, an apparatus for wireless communicationincludes a RF unit for transmitting and receiving radio signals, and aprocessor coupled with the RF unit and configured to receive a TPCindex, and acquire a TPC command from a plurality of TPC commands basedon the TPC index, wherein the plurality of TPC commands are included inthe downlink control information carried by the downlink control channeland the CRC parity bits of the downlink control information are maskedwith a TPC identifier.

In still another aspect, an apparatus for wireless communicationincludes a RF unit for transmitting and receiving radio signals, and aprocessor coupled with the RF unit and configured to receive a TPC indexand a TPC identifier, monitor at least one downlink control channel byattempting decoding of the at least one downlink control channel,acquire a TPC command on a downlink control channel based on the TPCindex when no CRC error is detected in the downlink control channel,wherein the CRC parity bits in the downlink control channel are maskedwith the TPC identifier, and adjust a transmit power of an uplinkchannel based on the TPC command.

In still another aspect, an apparatus for wireless communicationincludes a RF unit for transmitting and receiving radio signals, and aprocessor coupled with the RF unit and configured to monitor at leastone downlink control channel by attempting decoding of the at least onedownlink control channel, acquire a TPC command on a downlink controlchannel when no CRC error is detected in the downlink control channel,wherein the CRC parity bits in the downlink control channel are maskedwith a first TPC identifier or a second TPC identifier, adjust atransmit power of a first uplink channel based on the TPC command whenthe CRC parity bits in the downlink control channel are masked with afirst TPC identifier, and adjust a transmit power of a second uplinkchannel based on the TPC command when the CRC parity bits in thedownlink control channel are masked with a second TPC identifier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure of a wireless communication system.

FIG. 2 is a diagram showing functional split between an evolveduniversal terrestrial radio access network (E-UTRAN) and an evolvedpacket core (EPC).

FIG. 3 is a block diagram showing constitutional elements of a userequipment.

FIG. 4 is a diagram showing a radio protocol architecture for a userplane.

FIG. 5 is a diagram showing a radio protocol architecture for a controlplane.

FIG. 6 shows mapping between downlink logical channels and downlinktransport channels.

FIG. 7 shows mapping between uplink logical channels and uplinktransport channels.

FIG. 8 shows mapping between downlink transport channels and downlinkphysical channels.

FIG. 9 shows mapping between uplink transport channels and uplinkphysical channels.

FIG. 10 shows a structure of a radio frame.

FIG. 11 shows an example of a resource grid for one downlink slot.

FIG. 12 shows a structure of a subframe.

FIG. 13 is a flowchart showing a process of configuring a physicaldownlink control channel (PDCCH).

FIG. 14 shows an exemplary structure of a PDCCH for transmitting atransmit power control (TPC) command according to an embodiment of thepresent invention.

FIG. 15 is a flow diagram showing a transmit power control methodaccording to an embodiment of the present invention.

FIG. 16 shows a medium access control (MAC) protocol data unit (PDU)configured in a MAC layer.

FIG. 17 is a block diagram showing an apparatus for wirelesscommunication according to an embodiment of the present invention.

FIG. 18 is a flowchart showing a transmit power control method accordingto an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.The UTRA is a part of a universal mobile telecommunication system(UMTS). A third generation partnership project (3GPP) long termevolution (LTE) is a part of an evolved UMTS (E-UMTS) using the E-UTRA.The 3GPP LTE uses the OFDMA in downlink and uses the SC-FDMA in uplink.An LTE-advance (LTE-A) is an evolution of the 3GPP LTE.

For clarity, the following description will focus on the 3GPP LTE/LTE-A.However, technical features of the present invention are not limitedthereto.

FIG. 1 shows a structure of a wireless communication system. Thewireless communication system may have a network structure of anevolved-universal mobile telecommunications system (E-UMTS). Thewireless communication system can be widely deployed to provide avariety of communication services, such as voices, packet data, etc.

Referring to FIG. 1, an evolved-UMTS terrestrial radio access network(E-UTRAN) includes at least one base station (BS) 20 which provides acontrol plane and a user plane.

A user equipment (UE) 10 may be fixed or mobile, and may be referred toas another terminology, such as a mobile station (MS), a user terminal(UT), a subscriber station (SS), a wireless device, etc. The BS 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc. There are one ormore cells within the coverage of the BS 20. Interfaces for transmittinguser traffic or control traffic may be used between the BSs 20.Hereinafter, a downlink is defined as a communication link from the BS20 to the UE 10, and an uplink is defined as a communication link fromthe UE 10 to the BS 20.

The BSs 20 are interconnected by means of an X2 interface. The BSs 20are also connected by means of an S1 interface to an evolved packet core(EPC), more specifically, to a mobility management entity (MME)/servinggateway (S-GW) 30. The S1 interface supports a many-to-many relationbetween the BS 20 and the MME/S-GW 30.

FIG. 2 is a diagram showing functional split between the E-UTRAN and theEPC. Slashed boxes depict radio protocol layers and white boxes depictfunctional entities of the control plane.

Referring to FIG. 2, the BS performs the following functions: (1)functions for radio resource management (RRM) such as radio bearercontrol, radio admission control, connection mobility control, anddynamic allocation of resources to the UE; (2) Internet protocol (IP)header compression and encryption of user data streams; (3) routing ofuser plane data to the S-GW; (4) scheduling and transmission of pagingmessages; (5) scheduling and transmission of broadcast information; and(6) measurement and measurement reporting configuration for mobility andscheduling.

The MME performs the following functions: (1) non-access stratum (NAS)signaling; (2) NAS signaling security; (3) idle mode UE reachability;(4) tracking area list management; (5) roaming; and (6) authentication.

The S-GW performs the following functions: (1) mobility anchoring; and(2) lawful interception. A PDN gateway (P-GW) performs the followingfunctions: (1) UE IP allocation; and (2) packet filtering.

FIG. 3 is a block diagram showing constitutional elements of anapparatus for wireless communication. The apparatus may be a part of theUE. The apparatus includes a processor 51, a memory 52, a radiofrequency (RF) unit 53, a display unit 54, and a user interface unit 55.Layers of the radio interface protocol are implemented in the processor51. The processor 51 provides the control plane and the user plane. Thefunction of each layer can be implemented in the processor 51. Thememory 52 is coupled to the processor 51 and stores various parametersfor operation of the processor 51. The display unit 54 displays avariety of information of the apparatus 50 and may use a well-knownelement such as a liquid crystal display (LCD), an organic lightemitting diode (OLED), etc. The user interface unit 55 can be configuredwith a combination of well-known user interfaces such as a keypad, atouch screen, etc. The RF unit 53 is coupled to the processor 51 andtransmits and/or receives radio signals.

Layers of a radio interface protocol between the UE and the network canbe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. A physical layer, or simply a PHY layer, belongs to the firstlayer and provides an information transfer service through a physicalchannel. A radio resource control (RRC) layer belongs to the third layerand serves to control radio resources between the UE and the network.The UE and the network exchange RRC messages via the RRC layer.

FIG. 4 is a diagram showing a radio protocol architecture for the userplane. FIG. 5 is a diagram showing a radio protocol architecture for thecontrol plane. They illustrate the architecture of a radio interfaceprotocol between the UE and the E-UTRAN. The user plane is a protocolstack for user data transmission. The control plane is a protocol stackfor control signal transmission.

Referring to FIGS. 4 and 5, a PHY layer belongs to the first layer andprovides an upper layer with an information transfer service through aphysical channel. The PHY layer is coupled with a medium access control(MAC) layer, i.e., an upper layer of the PHY layer, through a transportchannel. Data is transferred between the MAC layer and the PHY layerthrough the transport channel. Between different PHY layers (i.e., a PHYlayer of a transmitter and a PHY layer of a receiver), data istransferred through the physical channel.

The MAC layer belongs to the second layer and provides services to aradio link control (RLC) layer, i.e., an upper layer of the MAC layer,through a logical channel. The RLC layer in the second layer supportsreliable data transfer. There are three operating modes in the RLClayer, that is, a transparent mode (TM), an unacknowledged mode (UM),and an acknowledged mode (AM) according to a data transfer method. An AMRLC provides bidirectional data transmission services and supportsretransmission when the transfer of the RLC protocol data unit (PDU)fails.

A packet data convergence protocol (PDCP) layer belongs to the secondlayer and performs a header compression function for reducing an IPpacket header size.

A radio resource control (RRC) layer belongs to the third layer and isdefined only in the control plane. The RRC layer serves to control thelogical channel, the transport channel, and the physical channel inassociation with configuration, reconfiguration and release of radiobearers (RBs). An RB is a service provided by the second layer for datatransmission between the UE and the E-UTRAN. When an RRC connection isestablished between an RRC layer of the UE and an RRC layer of thenetwork, it is called that the UE is in an RRC connected mode. When theRRC connection is not established yet, it is called that the UE is in anRRC idle mode.

A non-access stratum (NAS) layer belongs to an upper layer of the RRClayer and serves to perform session management, mobility management, orthe like.

FIG. 6 shows mapping between downlink logical channels and downlinktransport channels. FIG. 7 shows mapping between uplink logical channelsand uplink transport channels. This may be found in section 6.1.3 of the3GPP TS 36.300 V8.3.0 (2007-12) “Technical Specification Group RadioAccess Network; Evolved Universal Terrestrial Radio Access (E-UTRA) andEvolved Universal Terrestrial Radio Access Network (E-UTRAN); Overalldescription; Stage 2 (Release 8)”.

Referring to FIGS. 6 and 7, in downlink, a paging control channel (PCCH)is mapped to a paging channel (PCH). A broadcast control channel (BCCH)is mapped to a broadcast channel (BCH) or a downlink shared channel(DL-SCH). A common control channel (CCCH), a dedicated control channel(DCCH), a dedicated traffic channel (DTCH), a multicast control channel(MCCH), and a multicast traffic channel (MTCH) are mapped to the DL-SCH.The MCCH and the MTCH are also mapped to a multicast channel (MCH). Inuplink, the CCCH, the DCCH, and the DTCH are mapped to an uplink sharedchannel (UL-SCH).

A type of each logical channel is defined according to a type ofinformation to be transmitted. A logical channel is classified into twogroups, i.e., a control channel and a traffic channel.

The control channel is used for transmitting control plane information.The BCCH is a downlink control channel for broadcasting system controlinformation. The PCCH is a downlink channel for transmitting paginginformation and is used when a network does not know the location of theUE. The CCCH is a channel for transmitting control information betweenthe UE and the network and is used when there is no RRC connectionestablished between the UE and the network. The MCCH is apoint-to-multipoint downlink channel used for transmitting multimediabroadcast multicast service (MBMS) control information from the networkto the UE. The MCCH is used by UEs that receive an MBMS. The DCCH is apoint-to-point bi-directional channel for transmitting dedicated controlinformation between the UE and the network, and is used by UEs having anRRC connection.

The traffic channel is used for transmitting user plane information. TheDTCH is a point-to-point channel for transmitting user information. TheDTCH can exist in both uplink and downlink. The MTCH is apoint-to-multipoint downlink channel for transmitting traffic data andis used by the UEs that receive the MBMS.

The transport channel is classified according to a type andcharacteristic of data transmission through a radio interface. The BCHis broadcast in the entire coverage area of the cell and has a fixed,pre-defined transport format. The DL-SCH is characterized by support forhybrid automatic repeat request (HARQ), support for dynamic linkadaptation by varying modulation, coding, and a transmit power, apossibility to be broadcast in the entire cell, and a possibility to usebeamforming, support for both dynamic and semi-static resourceassignment, support for UE discontinuous reception (DRX) to enable UEpower saving, and support for MBMS transmission. The PCH ischaracterized by support for DRX to enable UE power saving andrequirement to be broadcast in the entire coverage area of the cell. TheMCH is characterized by support for requirement to be broadcast in theentire coverage area of the cell and support for an MBMS singlefrequency network (MBSFN).

The UL-SCH and a random access channel (RACH) are uplink transportchannels. The UL-SCH is characterized by support for dynamic linkadaptation for changing the modulation, coding, and a transmit power andsupport for HARQ and dynamic/semi-static resource assignment. The RACHis characterized by limited control information and collision risk.

FIG. 8 shows mapping between downlink transport channels and downlinkphysical channels. FIG. 9 shows mapping between uplink transportchannels and uplink physical channels.

Referring to FIGS. 8 and 9, in downlink, a BCH is mapped to a physicalbroadcast channel (PBCH). An MCH is mapped to a physical multicastchannel (PMCH). A PCH and a DL-SCH are mapped to a physical downlinkshared channel (PDSCH). The PBCH carries a BCH transport block. The PMCHcarries the MCH. The PDSCH carries the DL-SCH and the PCH. In uplink, aUL-SCH is mapped to a physical uplink shared channel (PUSCH). An RACH ismapped to a physical random access channel (PRACH). The PRACH carries arandom access preamble.

There are several physical control channels used in a PHY layer. Aphysical downlink control channel (PDCCH) informs the UE of resourceassignment of the PCH and DL-SCH, and also informs the UE of HARQinformation related to the DL-SCH. The PDCCH may carry an uplinkscheduling grant which informs the UE of resource assignment for uplinktransmission. A physical control format indicator channel (PCFICH)informs the UE of the number of orthogonal frequency divisionmultiplexing (OFDM) symbols used for the PDCCHs and is transmitted inevery subframe. A physical hybrid ARQ indicator channel (PHICH) carriesHARQ acknowledgement (ACK)/negative-acknowledgement (NACK) signals inresponse to uplink transmission. A physical uplink control channel(PUCCH) carries HARQ ACK/NACK signals in response to downlinktransmission, scheduling request, and uplink control information (e.g.,a channel quality indicator (CQI)).

FIG. 10 shows a structure of a radio frame.

Referring to FIG. 10, a radio frame includes 10 subframes. One subframeincludes two slots. A time for transmitting one subframe is defined as atransmission time interval (TTI). For example, one subframe may have alength of 1 millisecond (ms), and one slot may have a length of 0.5 ms.

The radio frame of FIG. 10 is shown for exemplary purposes only. Thus,the number of subframes included in the radio frame or the number ofslots included in the subframe or the number of OFDM symbols included inthe slot may change variously.

FIG. 11 shows an example of a resource grid for one downlink slot.

Referring to FIG. 11, the downlink slot includes a plurality of OFDMsymbols in a time domain. Although it is described herein that onedownlink slot includes 7 OFDM symbols and one resource block includes 12subcarriers in a frequency domain, this is for exemplary purposes only,and thus the present invention is not limited thereto.

Elements on the resource grid are referred to as resource elements. Oneresource block includes 12×7 resource elements. The number N^(DL) ofresource blocks included in the downlink slot depends on a downlinktransmission bandwidth determined in a cell.

FIG. 12 shows a structure of a subframe.

Referring to FIG. 12, the subframe includes two consecutive slots. Up tothree OFDM symbols located in a front portion of a 1^(st) slot withinthe subframe are included in a control region to be assigned with aPDCCH. The remaining OFDM symbols are included in a data region to beassigned with a PDSCH. A PCFICH carries information regarding the numberof OFDM symbols used to transmit PDCCHs within the subframe.

The PDCCH may carry a transport format related to the DL-SCH and thePCH, resource allocation information, and/or a transmit power control(TPC) command. A plurality of PDCCHs can be transmitted in the controlregion. The UE monitors the plurality of PDCCHs. The PDCCH may betransmitted on an aggregation of one or several contiguous controlchannel elements (CCEs). The CCEs correspond to a plurality of resourceelement groups. A PDCCH format and the number of bits of an availablePDCCH are determined according to the number of CCEs.

Control information transmitted through the PDCCH is referred to asdownlink control information (DCI). The DCI is used to transmit uplinkor downlink scheduling information or to transmit a TPC command foruplink power control. A DCI format includes a format 0 for transmissionof uplink shared channel (UL-SCH) allocation, a format 1 fortransmission of DL-SCH allocation for a single input multiple output(SIMO) operation, a format 1A for compact transmission of DL-SCHallocation for the SIMO operation, a format 2 for transmission of DL-SCHallocation for a multiple input multiple output (MIMO) operation, andformats 3 and 3A for transmission of a TPC command for an uplinkchannel.

Table 1 below shows information included in each DCI format.

TABLE 1 Format Information Format 0 UL-SCH assignment TPC command forPUSCH Format 1 DL-SCH assignment TPC command for PUCCH Format 1A DL-SCHassignment TPC command for PUCCH Format 2 DL-SCH assignment TPC commandfor PUCCH Format 3 TPC commands for UE 1, UE 2, . . . , UE N Format 3ATPC commands for UE 1, UE 2, . . . , UE 2N

The formats 0 to 2 correspond to control information for one UE andinclude a TPC command for an uplink channel. The formats 3 and 3Ainclude TPC commands for a plurality of UEs. Unlike the formats 0 to 2received by one UE, the formats 3 and 3A are received by the pluralityof UEs. The number of bits of the TPC command for the format 3 isdifferent from the number of bits of the TCP command for the format 3A.For example, if the format 3 includes a 2-bit TPC command for powercontrol, the format 3A includes a 1-bit TPC command for power control.In this case, regarding the same DCI size, the number of TPC commandsincluded in the format 3A is twice the number of TPC commands includedin the format 3.

FIG. 13 is a flowchart showing a process of configuring a PDCCH.

Referring to FIG. 13, in step S110, the BS determines a PDCCH formataccording to a DCI to be transmitted to the UE, and attaches cyclicredundancy check (CRC) parity bits to control information. A uniqueidentifier (i.e., a radio network temporary identifier (RNTI)) is maskedon the CRC parity bits according to a usage or an owner of the PDCCH. Ifthe PDCCH is for a specific UE, a unique identifier (e.g., cell-RNTI(C-RNTI)) of the UE can be masked on the CRC parity bits. If the PDCCHis for paging information, a paging indication-RNTI (PI-RNTI) can bemasked on the CRC parity bits. If the PDCCH is for system information, asystem information identifier (e.g., system information-RNTI (SI-RNTI))can be masked on the CRC parity bits. In order to indicate a randomaccess response that is a response for transmission of a random accesspreamble of the UE, a random access-RNTI (RA-RNTI) can be masked on theCRC parity bits. Table 2 below shows an example of identifiers masked onthe CRC parity bits of the PDCCH.

TABLE 2 Type Identifier Description UE-specific C-RNTI used for the UEcorresponding to the C-RNTI Common PI-RNTI used for paging messageSI-RNTI used for system information RA-RNTI used for random accessresponse

When using the C-RNTI, the PDCCH carries dedicated control informationfor a specific UE. When using other RNTIs, the PDCCH carries commoncontrol information to be received by all (or a plurality of) UEs in acell.

In step S120, channel coding is performed on the CRC-attached controlinformation to generate coded data. In step S130, rate matching isperformed according to the number of CCEs assigned to the PDCCH format.In step S140, the coded data is modulated to generate modulationsymbols. In step S150, the modulation symbols are mapped to physicalresource elements.

A plurality of PDCCHs can be transmitted in one subframe. The UEmonitors the plurality of PDCCHs. Monitoring is an operation in whichthe UE attempts decoding of the respective PDCCHs according to formatsof the monitored PDCCHs. In the control region assigned in the subframe,the BS does not provide information indicating a location of acorresponding PDCCH to the UE. The UE searches for its PDCCH bymonitoring a group of PDCCH candidates from a logical search spaceconfigured in the control region. For example, the UE performsde-masking on its C-RNTI from a corresponding PDCCH candidate, and it isregarded that the UE detects its PDCCH if a CRC error is not detected.

The search space is a logical space for searching PDCCH. The group ofPDCCH candidates to be monitored is defined according to the searchspace. If an aggregation of all CCEs for the PDCCH in one subframe isdefined as a CCE aggregation, the search space denotes an aggregation ofcontiguous CCEs starting at a specific starting position in the CCEaggregation according to an aggregation level. An aggregation level L isa CCE unit for PDCCH search. A size of the aggregation level L isdefined by the number of contiguous CCEs. The search space is definedaccording to the aggregation level. In the search space, the PDCCHcandidates are located with respect to every aggregation level size.

Now, transmit power control of a physical uplink shared channel (PUSCH)and a physical uplink control channel (PUCCH) in the LTE will bedescribed. This may be found in section 5.1 of the 3GPP TS 36.213 V8.2.0(2008-03) “Technical Specification Group Radio Access Network; EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical layer procedures(Release 8)”.

The transmit power P_(PUSCH) for the PUSCH transmission in a subframe iis defined by:

P _(PUSCH)(i)=min{P _(MAX),10 log₁₀(M _(PUSCH)(i))+P _(O) _(—)_(PUSCH)(i)+α·PL+Δ _(TF)(TF(i))+f(i)}  Equation 1

where P_(MAX) is the maximum allowed power that depends on the UE powerclass, M_(PUSCH)(i) is the size of the PUSCH resource assignmentexpressed in number of resource blocks valid for subframe i, P_(O) _(—)_(PUSCH)(j) is a parameter, α is a cell specific parameter, PL is thedownlink pathloss estimate calculated in the UE, Δ_(TF)(TF(i)) is aparameter, and f(i) is a current PUSCH power control adjustment statewhich is given by a UE specific correction value δ_(PUSCH) referred toas a TPC command.

The transmit power P_(PUCCH) for the PUCCH transmission in subframe i isdefined by:

P _(PUCCH)(i)=min{P _(MAX) , P _(O) _(—) _(PUCCH) +PL+Δ _(TF) _(—)_(PUCCH)(TF)+g(i)}  Equation 2

where P_(MAX) is the maximum allowed power that depends on the UE powerclass, P_(O) _(—) _(PUCCH)(j) is a parameter, PL is the downlinkpathloss estimate calculated in the UE, Δ_(TF) _(—) _(PUCCH)(TF) aregiven by RRC, and g(i) is the current PUCCH power control adjustmentstate which is given by a UE specific correction value δ_(PUCCH)referred to as a TPC command.

FIG. 14 shows an exemplary structure of a PDCCH for transmitting a TPCcommand according to an embodiment of the present invention.

Referring to FIG. 14, a TPC identifier (TPC-ID) is masked on CRC paritybits of DCI. The DCI includes TPC commands for a plurality of UEs. Forexample, the DCI may have the DCI format 3 or the DCI format 3A. TheTPC-ID is an identifier to be de-masked when one or more UEs monitor aPDCCH that carries the TPC command. The TPC-ID may be an identifier tobe used by a UE to decode the PDCCH in order to determine whether theTPC command is transmitted on the PDCCH.

Conventional identifiers (i.e., C-RNTI, PI-RNTI, SI-RNTI, and RA-RNTI)may be reused as the TPC-ID, or a new identifier may be defined as theTPC-ID.

The TPC-ID may be an identifier for a specific group of UEs in a cell toreceive TPC commands. Thus, the TPC-ID may be differentiated from theC-RNTI which is an identifier for a specific UE and be differentiatedfrom the PI-RNTI, SI-RNTI, and RA-RNTI which are identifiers for all UEsin the cell. When the DCI includes TPC commands for N UEs, the TPCcommands may be received by the N UEs. If the DCI includes TPC commandsfor all UEs in the cell, the TPC-ID may be an identifier for all UEs inthe cell.

A UE searches for the DCI masked with the TPC-ID by monitoring a groupof PDCCH candidates from a search space in a subframe. In this case, theTPC-ID may be found either in a common search space or in a UE-specificsearch space. The common search space is a search space searched by allUEs in the cell. The UE-specific search space is a search space searchedby a specific UE. If a CRC error is not detected when the TPC-ID isde-masked with respect to a corresponding PDCCH candidate, the UE canreceive the TPC command on the PDCCH.

A TPC-ID for a PDCCH that carries only a plurality of TPC commands maybe defined. The UE receives a TCP command on the PDCCH addressed by theTPC-ID. The TPC command is used to adjust a transmit power of an uplinkchannel. Therefore, transmission to the BS can be prevented from beingfailed due to incorrect power control, or interference to another UE canbe mitigated.

FIG. 15 is a flow diagram showing a transmit power control methodaccording to an embodiment of the present invention.

Referring to FIG. 15, in step S310, a BS transmits information regardinga TPC-ID to a UE. The BS can transmit the information regarding theTPC-ID by using at least one of a MAC message, an RRC message, and acontrol message on a PDCCH. The information regarding the TPC-ID may bea TPC-ID itself and/or information related to the TPC-ID. Theinformation related to the TPC-ID includes the TPC-ID itself and/or aTPC index indicating a TPC command of a corresponding UE among aplurality of TPC commands included in DCI. The BS can divide UEs in acell into at least one group, and can allocate the TPC-ID to each group.

The TPC-ID can be classified into a TPC-ID for a PUCCH and a TPC-ID fora PUSCH. This means that the TPC-ID to be used can be classifiedaccording to a type of an uplink channel that controls a transmit power.This also means that a first uplink channel and a second uplink channelcan use different TPC-IDs. Upon detection of the TPC-ID for the PUCCH,the UE uses a corresponding TPC command to control a transmit power ofthe PUCCH. Upon detection of the TPC-ID for the PUSCH, the UE uses acorresponding TPC command to control a transmit power of the PUSCH.

Since the number of bits of the TPC command may differ from one UE toanother, the TPC-ID can be classified according to the number of bits ofthe TPC command. For example, information may be necessary to identify aTPC-ID for the DCI format 3 and a TPC-ID for the DCI format 3A.

The TPC index indicates a TPC command for a given UE among a pluralityof TPC commands included in the DCI formats 3 and 3A. The TPC index mayhave a format of an index for the TPC command or may have a bitmapformat.

In step S320, the BS transmits TPC commands on the PDCCH. The UEmonitors the PDCCH. If a CRC error is not detected by performing CRCde-masking using the TPC-ID, the UE receives a TPC command on the basisof a TPC index from the TPC commands included in corresponding DCI.

In step S330, the UE adjusts a transmit power of the uplink channel byusing the received TPC command. According to the TPC-ID, a transmitpower of the PUCCH or the PUSCH can be adjusted.

Now, a method of transmitting information regarding a TPC-ID by a BS toa UE will be described.

In a first embodiment, the BS can transmit the information regarding theTPC-ID to the UE by using a MAC message.

FIG. 16 shows a MAC protocol data unit (PDU) configured in a MAC layer.

Referring to FIG. 16, the MAC PDU includes a MAC header, a MAC controlelement, and at least one MAC service data unit (SDU). The MAC headerincludes at least one subheader. Each subheader corresponds to the MACcontrol element and the MAC SDU. The subheader indicates a length andcharacteristic of the MAC control element or the MAC SDU. The MAC SDU isa data block delivered from an upper layer (e.g., RLC layer or RRClayer) of the MAC layer. The MAC control element is used to delivercontrol information of the MAC layer such as a buffer status report.

The information regarding the TPC-ID may be included in the MAC PDU in aformat of the MAC control element. The MAC control element of the TPC-IDincludes a format (F) field indicating a format of the TPC command, achannel (C) field indicating an uplink channel to which the TPC commandis applied, a TPC index indicating the TPC command of a corresponding UEamong a plurality of TPC commands, and the TPC-ID. The F field is 1-bitinformation indicating either the DCI format 3 or the DCI format 3A usedby a corresponding PDCCH. The C field is 1-bit information indicatingthe PUSCH or the PUCCH.

The information regarding the TPC-ID may be configured in variousformats, and there is no restriction on an order of each field or thenumber of bits of each field. Further, the MAC PDU may be configured byusing only some of the fields. For example, if the UE knows its TPC-IDin advance, the TPC-ID may be excluded in transmission.

In a second embodiment, the BS can transmit the information regardingthe TPC-ID to the UE by using an RRC message. The BS can report theinformation regarding the TPC-ID to the UE by using the RRC message whenan RRC connection is set up or reconfigured.

In a third embodiment, the BS can transmit the information regarding theTPC-ID to the UE through the PDCCH. The BS can transmit the informationregarding the TPC-ID in addition to uplink resource allocationinformation and/or downlink resource allocation information. Forexample, the information regarding the TPC-ID may be included in atleast one of the DCI formats 0, 1, 1A, and 2.

In a fourth embodiment, the BS can transmit the information regardingthe TPC-ID to the UE as a part of system information.

FIG. 17 is a block diagram showing an apparatus for wirelesscommunication according to an embodiment of the present invention. Anapparatus 700 may be a part of the BS. The apparatus 700 includes acontrol channel generator 710, a data channel generator 720, and atransceiver 730. The data channel generator 720 serves to process userdata, and transmits the processed user data to the UE through thetransceiver 730. The control channel generator 710 configures a controlchannel. The control channel generator 710 attaches CRC parity bits toDCI, and masks a TPC-ID on the CRC parity bits. The CRC-masked DCI istransmitted through the transceiver 730.

FIG. 18 is a flowchart showing a transmit power control method accordingto an embodiment of the present invention. This method can be performedby the UE. In step S810, the UE monitors a PDCCH. A CRC error checkingmay be detected by decoding the PDCCH. In step S820, the UE acquires aTPC command from the PDCCH where the CRC error is not detected. ThePDCCH where the CRC error is not detected is regarded by the UE as DCIincluding the TPC command of the UE. When the DCI includes a pluralityof TCP commands, the UE acquires its TPC command on the basis of a TPCindex. In step S830, the UE adjusts a transmit power of an uplinkchannel according to the TPC command. If the TPC-ID used in the PDCCHdetection is a first TPC-ID, the TPC command is used to control atransmit power of a first uplink channel (e.g., PUCCH). If the TPC-IDused in the PDCCH detection is a second TPC-ID, the TPC command is usedto control a transmit power of a second uplink channel (e.g., PUSCH).

A transmit power of an uplink channel is adjusted using a transmit powercontrol (TPC) command received on a downlink control channel. Therefore,interference with another user equipment may be mitigated and batteryconsumption of a user equipment can be reduced.

The present invention can be implemented with hardware, software, orcombination thereof. In hardware implementation, the present inventioncan be implemented with one of an application specific integratedcircuit (ASIC), a digital signal processor (DSP), a programmable logicdevice (PLD), a field programmable gate array (FPGA), a processor, acontroller, a microprocessor, other electronic units, and combinationthereof, which are designed to perform the aforementioned functions. Insoftware implementation, the present invention can be implemented with amodule for performing the aforementioned functions. Software is storablein a memory unit and executed by the processor. Various means widelyknown to those skilled in the art can be used as the memory unit or theprocessor.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims. The exemplary embodimentsshould be considered in descriptive sense only and not for purposes oflimitation. Therefore, the scope of the invention is defined not by thedetailed description of the invention but by the appended claims, andall differences within the scope will be construed as being included inthe present invention.

1. A method of controlling a transmit power of an uplink channel in awireless communication system, the method comprising: receiving downlinkcontrol information on a downlink control channel, wherein the downlinkcontrol information comprises at least one transmit power control (TPC)command and Cyclic Redundancy Check (CRC) parity bits of the downlinkcontrol information are masked with a TPC identifier; and adjusting thetransmit power of the uplink channel based on the at least one TPCcommand.
 2. The method of claim 1, wherein the downlink control channelis a Physical Downlink Control Channel (PDCCH).
 3. The method of claim1, wherein the uplink channel is a Physical Uplink Control Channel(PUCCH) or a Physical Uplink Shared Channel (PUSCH).
 4. The method ofclaim 3, wherein the PUCCH and the PUSCH use different TPC identifiers.5. The method of claim 1, wherein the TPC identifier is received from abase station.
 6. The method of claim 1, wherein the size of the TPCidentifier is 16 bits.
 7. The method of claim 1, wherein the downlinkcontrol information comprises a plurality of TPC commands.
 8. The methodof claim 7, further comprising: selecting the TPC command from among theplurality of TPC commands.
 9. The method of claim 8, wherein the TPCcommand is indicated by a TPC index.
 10. The method of claim 9, whereinthe TPC index is received from a base station.
 11. An apparatus forwireless communication, the apparatus comprising: a Radio Frequency (RF)unit for transmitting and receiving radio signals; and a processorcoupled with the RF unit and configured to: receive downlink controlinformation on a downlink control channel, wherein the downlink controlinformation comprises at least one transmit power control (TPC) commandand Cyclic Redundancy Check (CRC) parity bits of the downlink controlinformation are masked with a TPC identifier; and adjust a transmitpower of an uplink channel based on the at least one TPC command. 12.The apparatus of claim 11, wherein the downlink control informationcomprises a plurality of TPC commands and the processor is configured toselect the TPC command from among the plurality of TPC commands based onan index.
 13. A method of transmitting transmit power control (TPC)commands for controlling a transmit power of an uplink channel in awireless communication system, the method comprising: preparing downlinkcontrol information which comprises a plurality of TPC commands;attaching Cyclic Redundancy Check (CRC) parity bits to the downlinkcontrol information; masking the CRC parity bits with a TPC identifier;and transmitting the CRC-masked downlink control information.
 14. Themethod of claim 13, wherein the TPC identifier is used to identify userequipments to receive the plurality of TPC commands.
 15. The method ofclaim 13, wherein the TPC identifier is used to identify an uplinkchannel whose transmit power is adjusted.